A lawyer is not necessary but highly advisable. The process for getting a divorce is a particularly long and complicated one. Documents need to be served on the other party and to the court, and if one step is not completed properly it can cause massive delays.
Ask yourself if you have the time and energy to research the process, understand it completely and then execute it and the many steps involved over the next few months. You may also want to consider the cost of having to take time off work to complete these steps.